In an organic electroluminescence device, in order to reduce the operating voltage of the device, the injection of electrons and holes should be balanced. It is needed to improve electron injection ability.
The use of a low work function metal as a cathode can effectively improve electron injection ability. However, the low work function metal is too active and apt to react with water and oxygen.
Another method for improving electron injection ability is to add an electron injection layer formed of an inorganic compound layer between said cathode and an organic layer. It has been proved in practice that LiF/Al is a cathode structure having excellent electron injection ability, which is widely used in OLED products. However, the present of halogen elements may cause quench of light emission.